CVE-2026-68138net/sched: serialize qdisc_rtab_list against concurrent get/put

Official description

In the Linux kernel, the following vulnerability has been resolved: net/sched: serialize qdisc_rtab_list against concurrent get/put qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly linked list qdisc_rtab_list and a plain non-atomic 'int refcnt' with no lock. This was only safe because every caller historically held the RTNL mutex, which serialized all rate-table lookups, inserts and frees. That invariant no longer holds. cls_flower sets TCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false for it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through tcf_exts_validate_ex() -> tcf_action_init() -> tcf_action_init_1() -> tcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the RTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each adding a flower filter with a police action carrying the same rate, then race on qdisc_rtab_list and on the non-atomic refcnt, leading to a use-after-free / double-free of the kmalloc-2k struct qdisc_rate_table. qdisc_rtab_list is a single global (not per-netns), so the corrupted object is shared system-wide. BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160 qdisc_put_rtab+0x12f/0x160 tcf_police_init+0xda9/0x1590 tcf_action_init_1+0x460/0x6b0 tcf_action_init+0x439/0xa40 tcf_exts_validate_ex+0x42d/0x550 fl_change+0xddd/0x7da0 tc_new_tfilter+0xaa7/0x2420 rtnetlink_rcv_msg+0x95e/0xe90 which belongs to the cache kmalloc-2k of size 2048 Protect qdisc_rtab_list and the refcount with a dedicated spinlock. The (sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before taking the lock; if a concurrent inserter added an identical table in the meantime the freshly allocated one is freed under the lock, so no duplicate is leaked. qdisc_put_rtab() now decrements the refcount and unlinks under the same lock.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/1b050d09dd1a0ddae83bf012cf4956b7a960235f
• https://git.kernel.org/stable/c/6e0241f6cbb149d926ee8efee2c734fea71452cf
• https://git.kernel.org/stable/c/f93c89392bd3b180b5b7abc6fdae8e3dd667a313
• https://git.kernel.org/stable/c/4131dd0b6f67acddd616ed7c244e1d3eedd46e7b
• https://git.kernel.org/stable/c/d981098b76756ed71666a27518eeb69883657c43
• https://git.kernel.org/stable/c/8ddc2eb0d2da9c83f54f1e5720525b461b8480c4
• https://git.kernel.org/stable/c/fb29e1b41052488ee3f2d115d4a870497ebd7f7d
• https://git.kernel.org/stable/c/f43ee0c0730d6191629b5ee1ceae27b1ebfdc047